Dual-wavelength thermal infrared sensor

Abstract

A dual-wavelength thermal infrared sensor includes a first and a second type pixels that detect infrared in different wavelength ranges. The pixels of both types include a diaphragm supported by beams, an eave formed to spread outward from the diaphragm, and reflection film on the substrate. The diaphragm includes a thermoelectric conversion material thin film, an electrode, and protective films. The protective films and eaves are made of a material having larger absorption coefficient for infrared in the first wavelength range and a smaller absorption coefficient for infrared in second wavelength range. First-type pixels further have metal thin films formed on the top of the diaphragm and eaves. First-type pixels have sensitivity to infrared in a first wavelength range and in a second wavelength range defined by optical interference occurring between the metal thin films and the reflection film. Second-type pixels have sensitivity to first wavelength range infrared.

1. A dual-wavelength thermal infrared sensor that has a thermal insulation structure and comprises a plurality of pixels that detect incident infrared rays,
 wherein the plurality of pixels include pixels of a first type and pixels of a second type that detect infrared rays in different wavelength ranges, 
 the pixel of the first type and the pixel of the second type each include a diaphragm that is supported by beams extending from a substrate to have a gap from the substrate; an eave that is formed to spread outward from the diaphragm; and a reflection film that substantially reflects infrared rays and exists on the substrate immediately beneath the diaphragm, the diaphragm includes: a thermoelectric conversion material thin film that is substantially transmissive to infrared rays; an electrode that catches a change of a physicality of the thermoelectric conversion material thin film; and protective films that enclose the thermoelectric conversion material thin film and the electrode, and the protective films of the diaphragm and the eave are made of a material that has a relatively large absorption coefficient for infrared rays in a first wavelength range and a relatively small absorption coefficient for infrared rays in a second wavelength range different from the first wavelength range, 
 the pixel of the first type further includes metal thin films that are formed on an upper surface of the diaphragm and an upper surface of the eave respectively; 
 the pixel of the first type has sensitivity to infrared rays in the first wavelength range that are absorbed by the protective films and the eave, and to infrared rays in the second wavelength range that is defined by an optical interference that occurs between the metal thin films and the reflection film, and 
 the pixel of the second type has sensitivity to infrared rays in the first wavelength range that are absorbed by the protective films and the eave. 
 
     
     
       2. The dual-wavelength thermal infrared sensor according to  claim 1 ,
 wherein the thermoelectric conversion material thin film is a bolometer material thin film, and the change of the physicality is a change of resistance. 
 
     
     
       3. The dual-wavelength thermal infrared sensor according to  claim 1 ,
 wherein the first wavelength range is a wavelength range of 8 to 14 μm, and the second wavelength range is an infrared wavelength range of 8 μm or shorter. 
 
     
     
       4. The dual-wavelength thermal infrared sensor according to  claim 1 ,
 wherein the material of the protective films and the eave is silicon nitride film, the first wavelength range is a wavelength range of 8 to 14 μm, and the second wavelength range is a wavelength range of 3 to 5 μm. 
 
     
     
       5. A method for acquiring image, comprising: disposing pixels of a first type and pixels of a second type that detect infrared rays in different wavelength ranges in a staggered arrangement, row by row, or column by column, wherein the pixel of the first type and the pixel of the second type each includes a diaphragm that is supported by beams extending from a substrate to have a gap from the substrate; an eave that is formed to spread outward from the diaphragm; and a reflection film that substantially reflects infrared rays and exists on the substrate immediately beneath the diaphragm, wherein the diaphragm includes: a thermoelectric conversion material thin film that is substantially transmissive to infrared rays; an electrode that catches a change of a physicality of the thermoelectric conversion material thin film; and protective films that enclose the thermoelectric conversion material thin film and the electrode, wherein the protective films of the diaphragm and the eave are made of a material that has a relatively large absorption coefficient for infrared rays in a first wavelength range and a relatively small absorption coefficient for infrared rays in a second wavelength range different from the first wavelength range; forming metal thin films on an upper surface of the diaphragm and an upper surface of the eave respectively of the pixel of the first type; acquiring an image of infrared rays in the first wavelength range from signals output by the pixels of the second type that has sensitivity to infrared rays in the first wavelength range that are absorbed by the protective films and the eave; and subtracting a value obtained by multiplying signals output by the pixels of the second type by a predetermined coefficient from signals output by the pixels of the first type having sensitivity to infrared rays in the first wavelength range that are absorbed by the protective films and the eave, and sensitivity to infrared rays in the second wavelength range that is defined by an optical interference that occurs between the metal thin films and the reflection film.